The field of semiconductor processing has been facilitated by the use of plasma reactors, and similar equipment. In fabricating semiconductor integrated circuits, plasma reactor equipment is employed for depositing layers or films of conductive material, semiconductor material, or insulating materials in various patterns, configurations, and thicknesses to form microcircuits. Dry etching of semiconductor materials can also be conducted with chemical vapor transport systems to selectively remove desired areas of such materials to form the requisite patterns or configurations. The use of these aforementioned equipment often requires various gases to be introduced into a contained environment into which a semiconductor wafer has been placed to form microcircuits. Typically, the contained environment is a plasma chamber of the equipment. The gas is desired to be uniformly distributed over the surface of the semiconductor wafer inside the chamber for purposes of deposition, etch, or another wafer fabrication process. The reason for desiring uniform gas distribution is that variations in the gas flow across the surface of the wafer result in nonuniform deposition or etch causing nonplanar topography which can lead to yield loss, incomplete etch, and consequently device failures.
The current accepted method of distributing the flow of gases in a plasma chamber is through the use of multistage gas dispersion disks. One such gas dispersion disk is shown in FIG. 1, wherein the disk 10 has a plurality of holes 12 in the disk. The holes 12 are in practice drilled in precise locations per a specific hole pattern. The specific hole patterns are proprietary to each semiconductor device manufacturer because the hole patterns are typically experimentally determined to yield the most uniform gas distribution for that company's plasma reactor equipment configuration.
Multiple gas dispersion disks are currently used together to more evenly diffuse the incoming gas, as illustrated in FIG. 2, which is a cross-sectional schematic of a plasma reactor 14. The plasma reactor 14 has a reactor chamber 16 which contains a semiconductor wafer 18 supported by a susceptor or pedestal 20. There is a gas inlet 22 at the top of the reactor chamber 16. The incoming gas is dispersed through two gas dispersion disks, wherein the top disk 10 will be referred to as a blocker plate or a pre-diffuser, and the bottom disk 24 will be referred to as a face plate or electrode. Often, the holes 26 in the face plate 24 are tapered, as illustrated, to better disperse the gas exiting holes 26 which are themselves positioned above the surface of the semiconductor wafer 18. Alternatively, the holes can be counterbored such that the top portion of holes are larger than the bottom portion at the exit surface.
This gas dispersion technique has several disadvantages. One disadvantage is that these plates with the company proprietary hole patterns are very expensive due to the manufacturing process required to drill the holes. Furthermore, these plates are often made of anodized aluminum for increased life, and the anodization process itself is costly. Additionally, an increase in the diameter of the semiconductor wafer exacerbates the nonuniform flow problems especially at the edges of the wafer. For example, the gas flow may be laminar at the center of the wafer surface but is turbulent at the edges. Furthermore, process drift occurs over time and the flow pattern changes leading to variability in the process. In addition, the holes clog after a time in manufacturing leading to undesirable flow patterns and results. Yet another problem is that multiple gas dispersion disks must be used in order to more evenly distribute the gas, but the fluid flow dynamics become extremely difficult to accurately model to determine the optimum patterns to achieve laminar flow. Added to this problem is the difficulty in alignment of multiple disks to get the various hole patterns aligned correctly with respect to each other to achieve laminar flow. Furthermore, in etch, the face plates erode over time so they have to be replaced which adds yet another area of variability in the process where tight process control is critical due to the submicron dimensions involved in building microcircuits.
Thus, a need exists for being able to uniformly distribute gas for any semiconductor process requiring laminar flow over a large surface area without needing expensive plates having proprietary hole patterns which are costly and inefficient.